Modules

Modules are used to split up logic in an application. A module is just a file in JavaScript.

Modules can be imported and exported using the keywords import and export.

CommonJS

CommonJS is the default for Node.js. By using CommonJS, modules are exported using module.exports = function() {} and imported using the require syntax const {add} = require('./script');

module.exports.add = function(a, b) {
  return a + b;
}

module.exports.subtract = function(a, b) {
  return a - b;
}

----

const {add, subtract} = require('./util')

console.log(add(5, 5)) // 10
console.log(subtract(10, 5)) // 5

ES Modules (ECMAScript 2015 / ES6)

With ES6, import and export statements were added to allow more efficient tree-shaking builds and support fro==or both static and dynamic imports.

export const add = (x, y) => x + y;
export const subtract = (x, y) => x - y;

----

import { add } from './math.js';
console.log(add(2, 3)); // Output: 5

Default vs Named Import

CommonJS

module.exports.namedFunction = function () {};
module.exports = { namedFunction };

----

const defaultFunction = require('./');
defaultFunction.namedFunction();

or

const { namedFunction } = require('./');
namedFunction();

ES Modules

export const namedFunction = () => {}
export default function() => {}

----

import { namedFunction } from './';
namedFunction();

import defaultFunction from './';
defaultFunction();

import * as allNamedFunctions from './';
allNamedFunction.namedFunction();

Differences

Feature	require	import
Module System	CommonJS	ES6 (ECMAScript version 6)
Loading Type	Synchronous (modules are imported sequentially)	Mostly static (modules are loaded in order at compile time, dynamic import is async)
Performance	Less efficient due to synchronous loading	More efficient with static imports due to predictability and async with dynamic imports
Memory Usage	Imports entire module, leading to potentially higher memory usage	Can import selective components, reducing memory usage
Export Access	Access to components exported by module.exports	Access to components exported by export
Implementation	Can be used directly as it is the default method in Node.js	Requires ES6 or ECMAScript module support enabled
Usage in Code	Can be used anywhere in the program	Static imports are used at the top, dynamic can be used within the program